Experimental data acquisition and Finite Element Analysis of kinetic aspects of functional occlusion in order to optimize dental reconstrucions
Final Report Abstract
In the clinical part of the project we recorded synchronously, for the first time, the electromyographic activity of all twelve main chewing muscles, the kinematics, and the chewing forces of the lower jaw during the comminution of natural test food. Sixteen healthy subjects completed the experimental protocol successfully and without complications. The data obtained from an asymptomatic test subject and the recorded MRI images were used to validate the FE model. Thus, the occlusal micromovements between antagonistic molars during chewing could be simulated realistically. Furthermore, the results serve to better understand the cocontraction patterns of all major masticatory muscles during the chewing cycle. In the numerical modelling part of the cooperative project, several numerical studies were performed using a finite element model of the masticatory system in order to obtain knowledge that would improve the planning of dental prostheses. As a primary goal, a sophisticated bolus that would undergo large deformation and fracture, in order to allow the antagonistic teeth to come into near occlusion, was developed. Additionally, the activation levels of the muscles, which were experimentally measured in the clinical part of the project, were processed and calibrated to produce the complicated chewing motion in the finite element model of the human mandible. The model was furthermore, modified to match the geometries of individual patients with a simplified approach by adjusting the mesh of the finite element model to match the geometries of the different patients. The same activation levels used to produce the chewing motion were employed with the modified models. Finally, a parametric study was carried out for different components of the masticatory system, to study their role and their influence on the behavior of the masticatory system. The specific findings of this project are summarized as follows: Despite the direct employment of EMG activation levels resulting in fairly accurate results for static biting forces, the measured EMG levels during mastication required a considerable amount of calibration before the results were considered satisfactory. This corroborates the difficulty to interpret the EMG levels of the muscles during movement. - During mastication, the contralateral joint handles a much larger load than the ipsilateral joint. Forces on the ipsilateral joint increase very slowly as the biting force raises. - The employment of activation levels to produce a specific biting force on models with a modified geometry, result in almost identical reaction forces on the joints. Although the motions of the jaw of the different modified models are similar for the same activation levels of the muscles, the variations in motion result in interference from teeth that are not involved in the mastication process. - The creation of custom-made models for patients remains very challenging, as significant calibration remains necessary. However, once a model has been properly set up, modifications can be incorporated (e.g. implants) to determine its impact on the overall behavior of the system. - Variation of material parameters of the soft tissues such as the articular disc and the periodontium, has minimal effect on the displacement and resulting forces. However, as the tissues become more incompressible, the stresses are reduced as the forces are more evenly distributed. - The jaw border movements are constrained by the attachments of the disc, the ligaments and the passive response of the muscles. The parameters shown in the literature for these tissues, were found to be too stiff to allow for the movements observed during experimental measurements. - With the current model, existing treatments can be studied in order to optimize them. Additionally, the proof-of-principle of a new treatment can be analyzed. Of particular interest, is the current search of criteria for the design of dental implant crowns, which involves the minimal movements of the teeth in the close-up range with respect to the jaws.
Publications
- "Realistic kinetic loading of the jaw system during single chewing cycles: a finite element study". 10. Jahrestagung der Deutschen Gesellschaft für Biomechanik (DGfB), Hannover, Germany (2017)
S. Martinez, H. J. Schindler, J. Lenz and K. Schweizerhof
- "Realistic kinetic loading of the jaw system during single chewing cycles: a finite element study". Journal of Oral Rehabilitation, 44(5):375-384. (2017)
S. E. Martinez Choy, J. Lenz, K. Schweizerhof, M. Schmitter and H. J. Schindler
(See online at https://doi.org/10.1111/joor.12501) - "A Comprehensive Finite Element Model of the Human Masticatory System". Institut für Mechanik, Fakultät für Bauingenieur-, Geo- und Umweltwissenschaften (BGU), Karlsruhe (2018)
S. E. Martinez Choy
- "Behavior of the periodontium under loading using a kinetic model of the masticatory system". 41st Solid Mechanics Conference. Warsaw, Poland (2018)
S. Martinez, H. J. Schindler, J. Lenz and K. Schweizerhof
- "Effects of introducing gap constraints in the masticatory system: A finite element study". Biodental Engineering V, (2018)
S. E. Martinez Choy, J. Lenz, K. Schweizerhof, and H. J. Schindler
(See online at https://doi.org/10.1201/9780429265297-2)
